(1) Field of the Invention
The present invention lies in the field of rotorcraft and it relates more particularly to ways of supplying fuel to a power plant of the rotorcraft.
The present invention relates to an architecture for supplying fuel to a multi-engined power plant of a rotorcraft that supplies mechanical power at least for driving at least one rotor of the rotorcraft.
(2) Description of Related Art
Rotorcraft are rotary wing aircraft having one or more rotors providing the rotorcraft at least with lift, and possibly also with propulsion and/or guidance in flight. Rotorcraft are also provided with various auxiliary members that consume mechanical power, such as compressors, electricity generators, and/or a ventilation, heating, and/or air conditioning installation, for example.
In this context, rotorcraft have a power plant comprising one or more fuel-burning engines, in particular turboshaft engines, comprising one or more main engines and also an auxiliary engine, commonly referred to as an auxiliary power unit (APU). Such rotorcraft are described in particular by the Applicant in Document CA 2 831 706 A1.
The main engines are typically dimensioned to deliver the mechanical power needed for driving the various members of the rotorcraft that consume mechanical power in flight, and in particular the rotor(s) and said auxiliary members. To this end, at least the main engines are engaged with a mechanical power transmission train from which the various members of the rotorcraft that consume mechanical power are driven.
The auxiliary power unit is typically dimensioned to deliver the mechanical power needed for driving the auxiliary members while the rotorcraft is on the ground. For this purpose, the auxiliary power unit is engaged with the mechanical power transmission train while usually being excluded from being engaged mechanically with the rotor(s) of the rotorcraft, given that its use is conventionally reserved for driving auxiliary members when the rotorcraft is not in flight.
In a particular category of rotorcraft, commonly referred to as “category A”, the power plant has a plurality of main engines acting simultaneously to provide the mechanical power needed by the rotorcraft in flight. Rotorcraft of category A are allowed to overfly sensitive territories, providing at least one main engine has the ability on its own to supply the mechanical power needed by the rotorcraft in flight in the event of a failure of one of the main engines of the power plant.
In this context, a category A rotorcraft is authorized to overfly a sensitive territory providing that the means that enable the main engines to operate individually on their own are separate. In the event of a failure of one of the main engines because its operation is faulty, at least one other main engine must be capable of driving said at least one rotor without its own operation being hampered by the failure of the faulty main engine.
This applies in particular to the ways in which fuel are supplied to the various main engines of the power plant. For this purpose, category A rotorcraft are typically provided with an installation for supplying fuel to the power plant that combines a plurality of fuel supply assemblies that are respectively allocated to feeding fuel individually to the various main engines.
Conventionally, the various fuel feed assemblies are isolated from one another in fluid flow terms. Each fuel feed assembly typically has a fuel tank, possibly made up of one or more fuel reserves in fluid flow communication with one another, and a fluid flow circuit suitable for conveying fuel from the tank to the associated main engine.
The main engines are conventionally fed individually with fuel via main pumps that are driven by the main engines. More particularly, when considering a given fuel supply assembly, the fluid flow circuit comprises at least one or more pipes and a said main pump driven by the main engine. The main pump sucks fuel from the tank in order to convey it to the main engine via a feed duct of the fluid flow circuit.
In addition, each of the fuel supply assemblies may also have at least one booster pump immersed in the tank for delivering fuel to the main engine in order to initiate its starting.
There arises a problem of fuel tanks possibly running out of fuel, e.g. as a result of fuel leaking from a faulty tank or as a result of the main engine associated with the tank consuming all of the fuel that was initially contained in that tank.
That is why it is common practice for each of the tanks to be provided with a feeder of predefined capacity. For a given fuel assembly, the feeder provides a reserve of fuel that enables the main engine to operate for a determined duration in the event of the tank running out of fuel.
The feeder is conventionally arranged inside the fuel tank and it is fed with fuel by at least one transfer pump. The transfer pump(s) convey(s) fuel continuously from the tank to the feeder, and the feeder has an overflow for returning excess fuel to the tank.
These provisions are such that the feeder is kept full of fuel providing fuel remains within the tank. In the event of the tank running out of fuel, the main engine can continue to operate for a duration that is predetermined by the capacity of the feeder.
Where appropriate, and in order to reduce the number of fluid flow members used by the fuel supply installation, the transfer pump(s) of a given fuel supply assembly may also be used to form said booster pump.
It is also common practice to provide a cross-feed circuit between the various tanks of the fuel supply installation in order to enable fuel to be exchanged between the tanks, in particular for the purpose of balancing the distribution of the weight of the fuel on board the rotorcraft. Providing a fluid flow member incorporated in the cross-feed circuit is activated, fuel from one tank can be used for maintaining an available quantity of fuel in another tank, or at least in the feeder associated with that other tank.
For information about a technological environment close to the present invention, reference may be made for example to Document EP 2 567 896 (Eurocopter), which describes a fuel supply installation for a twin-engined rotorcraft. Nevertheless, in that document, nothing states nor suggests using an auxiliary power unit in addition to the two main engines for driving a main rotor. Such a document therefore does not describe supplying fuel to such an auxiliary power unit.
In general manner, it is always desirable to simplify the organization of equipment on board rotorcraft, in particular in order to reduce the cost associated with designing, installing, and maintaining such equipment, and also for the purpose of reducing the overall weight of rotorcraft.
Such a search for simplification applies, amongst other things, to installations for supplying fuel to a power plant of a rotorcraft, as mentioned in Document EP 2 567 896.
Nevertheless, such a search for simplification must comply with flying safety constraints on category A multi-engined rotorcraft, in particular in the event of one of the tanks running out of fuel and/or in the event of one of the main engines failing.
Concerning the auxiliary power unit, it may have an auxiliary assembly for feeding it with fuel, which assembly may be of simplified architecture, given that its function is conventionally reserved to driving auxiliary members while the rotorcraft is on the ground. Such a simplified architecture for the auxiliary fuel supply assembly makes it possible in particular to use a single auxiliary fuel supply pump for the auxiliary power unit and taking fuel from a fuel tank that is specifically reserved for feeding fuel to the auxiliary power unit, or else from one of the tanks for feeding fuel to a main engine.
It may nevertheless be most advantageous also to make use of the auxiliary power unit in flight for the purpose of contributing to driving the rotor(s) of the rotorcraft, so as to deliver extra mechanical power under special flying circumstances in which a large amount of mechanical power is required, such as hovering, during takeoff or landing, or indeed in the event of one of the main engines failing, for example.
Nevertheless, under such circumstances, the auxiliary power unit remains mechanically engaged with the main power transmission train in order to contribute to driving the rotor(s) of the rotorcraft, even if its contribution is small. In such a context and given the specific constraints on category A rotorcraft, the auxiliary power unit must be capable of operating independently in the event of one of the main engines failing, in particular concerning the way in which the auxiliary power unit is supplied with fuel.
Furthermore, as described in Document EP 2 524 871 A1, it is also known to provide an aircraft with two main engines and an auxiliary power unit. Such an aircraft also has main tanks for feeding the two main engines with fuel. The auxiliary power unit is fed with fuel from an auxiliary tank housed inside one of the main tanks.
Nevertheless, under such circumstances, the main tanks do not have feeders. Furthermore, the auxiliary pump(s) for feeding the auxiliary power unit with fuel is/are housed in only one of the main tanks.
In this context, it is desirable to seek a solution for installing an assembly for supplying fuel that is reserved for the auxiliary power unit, while also coming within the above-mentioned search for simplifying the fuel feed architecture for the power plant, and while complying with the constraints associated with supplying fuel to the engines of a category A multi-engined rotorcraft that are mechanically engaged with the rotor(s) of the rotorcraft.
The present invention thus lies in the context of searching for such a solution on the basis of the above observation from which the approach of the present invention stems.
In the context of the auxiliary power unit possibly participating in providing some of the drive for the rotor(s) of the rotorcraft, conventional prejudices in the field of aviation need to be overcome in order to provide viable and safe ways of supplying fuel to the auxiliary power unit, while avoiding as much as possible adding complexity to the architecture of the installation for supplying fuel to the power plant.
It is found in practice that such prejudices go against using the auxiliary power unit for providing any participation in the driving of the rotor(s) of a category A multi-engined rotorcraft because of the extra complexity that arises in the architecture for feeding fuel to the power plant.
The difficulty of such an approach is to be seen in particular when said multi-engined rotorcraft is a twin-engined rotorcraft, i.e. a rotorcraft having a power plant with two of said main fuel-burning engines each of dimensions suitable for individually driving the rotor(s) of the rotorcraft in flight in the event of a failure of one of the main engines.
In such a context, in the event of one of the main engines failing, only one main engine is available for providing the mechanical power needed to keep the rotorcraft in flight under safe flying conditions, since the auxiliary power unit is incapable on its own of providing the drive required by the rotor(s) of the rotorcraft.